use FOLLY_HAVE_BACKTRACE to guard execinfo.h and usage of backtrace(3)

Summary:
FOLLY_USE_SYMBOLIZER is a poor guard for the existence of execinfo.h
and backtrace(3), which is widely available on unix platforms, but not
available on Android NDK. Instead, introduce FOLLY_HAVE_BACKTRACE and
have CMake detect its availability.

Reviewed By: yfeldblum, luciang

Differential Revision: D23361495

fbshipit-source-id: 4409363f3eaa754977a93e1f006c5911d8e32020

CMake/folly-config.h.cmake

@@ -70,6 +70,7 @@
 #cmakedefine FOLLY_HAVE_LIBUNWIND 1
 #cmakedefine FOLLY_HAVE_DWARF 1
 #cmakedefine FOLLY_HAVE_ELF 1
+#cmakedefine FOLLY_HAVE_BACKTRACE 1
 #cmakedefine FOLLY_USE_SYMBOLIZER 1
 #define FOLLY_DEMANGLE_MAX_SYMBOL_SIZE 1024
 

folly/experimental/symbolizer/StackTrace.cpp

@@ -28,7 +28,7 @@
 #include <libunwind.h>
 #endif
 
-#if FOLLY_USE_SYMBOLIZER
+#if FOLLY_HAVE_BACKTRACE
 #include <execinfo.h>
 #endif
 
@@ -54,7 +54,7 @@ ssize_t getStackTrace(
 #if FOLLY_HAVE_LIBUNWIND && defined(UNW_VERSION)
   int r = unw_backtrace(reinterpret_cast<void**>(addresses), maxAddresses);
   return r < 0 ? -1 : r;
-#elif FOLLY_USE_SYMBOLIZER
+#elif FOLLY_HAVE_BACKTRACE
   int r = backtrace(reinterpret_cast<void**>(addresses), maxAddresses);
   return r < 0 ? -1 : r;
 #else

folly/experimental/symbolizer/Symbolizer.cpp

@@ -35,6 +35,10 @@
 #include <folly/portability/SysMman.h>
 #include <folly/portability/Unistd.h>
 
+#if FOLLY_HAVE_BACKTRACE
+#include <execinfo.h>
+#endif
+
 #if FOLLY_HAVE_ELF
 #include <link.h>
 #include <ucontext.h>
@@ -271,6 +275,27 @@ void SafeStackTracePrinter::printSymbolizedStackTrace() {
   printer_.println(*addresses_, 2);
 }
 
+void SafeStackTracePrinter::printUnsymbolizedStackTrace() {
+  print("(safe mode, symbolizer not available)\n");
+#if FOLLY_HAVE_BACKTRACE
+  // `backtrace_symbols_fd` from execinfo.h is not explicitly
+  // documented on either macOS or Linux to be async-signal-safe, but
+  // the implementation in
+  // https://opensource.apple.com/source/Libc/Libc-1353.60.8/ appears
+  // safe.
+  ::backtrace_symbols_fd(
+      reinterpret_cast<void**>(addresses_->addresses),
+      addresses_->frameCount,
+      fd_);
+#else
+  AddressFormatter formatter;
+  for (size_t i = 0; i < addresses_->frameCount; ++i) {
+    print(formatter.format(addresses_->addresses[i]));
+    print("\n");
+  }
+#endif
+}
+
 void SafeStackTracePrinter::printStackTrace(bool symbolize) {
   SCOPE_EXIT {
     flush();
@@ -282,12 +307,7 @@ void SafeStackTracePrinter::printStackTrace(bool symbolize) {
   } else if (symbolize) {
     printSymbolizedStackTrace();
   } else {
-    print("(safe mode, symbolizer not available)\n");
-    AddressFormatter formatter;
-    for (size_t i = 0; i < addresses_->frameCount; ++i) {
-      print(formatter.format(addresses_->addresses[i]));
-      print("\n");
-    }
+    printUnsymbolizedStackTrace();
   }
 }
 

folly/experimental/symbolizer/Symbolizer.h

@@ -196,6 +196,7 @@ class SafeStackTracePrinter {
 
  protected:
   virtual void printSymbolizedStackTrace();
+  void printUnsymbolizedStackTrace();
 
  private:
   static constexpr size_t kMaxStackTraceDepth = 100;